The invention relates to a coating apparatus and method for applying a uniform coating on a substrate. More specifically, the invention relates to an apparatus and method for providing a uniform coating on a substrate having a surface geometry, such as a medical device.
Medical devices are becoming increasingly complex in terms of function and geometry. Traditional coating methods, such as dip coating, are often undesirable for coating these complex geometries since coating solution may get entrapped in the device structure. This entrapped solution may cause webbing or bridging of the coating solution and may hinder the device function.
Spray coating techniques have also been used to apply coatings to medical devices. However, current methods of spray coating have introduced operator error, and have resulted in reduced coating consistency and reduced coating efficiency.
The invention provides a device and method for applying a coating onto a substrate having surface geometry. The invention is particularly useful for such substrates as medical devices, since such devices are often relatively small in size and can include complex surface configurations. Preferably, the invention is used to coat such medical devices as stents or other devices involving coils, coiled portions or cylinders having cut stent patterns.
A preferred device of the invention includes a rotation member rotatable about a central axis; a plurality of substrate mounts positioned on the rotation member, the substrate mounts being rotatable about second axes; and a drive arrangement for rotating the rotation member about the central axis and rotating the substrate mounts about the second axes. In one embodiment, the rotation member is a wheel. In one embodiment, the second axes extend radially from the central axes, and the drive arrangement rotates the substrate mounts about radial axes. In another aspect, the device of the invention includes a plurality of substrate mounts that are rotatable about second axes that are parallel to the central axis.
A preferred method of the invention includes the following steps. A substrate holder is provided that includes a rotation member rotatable about a central axis, a plurality of substrate mounts positioned on the rotation member, and a drive arrangement for rotating the rotation member about a central axis and rotating the substrate mounts about radial axes. At least one coating station is provided adjacent to the rotation member, so that substrate mounts can be passed in proximity to the coating station or stations. The coating station includes a nozzle for delivery of a coating solution to the substrate surface, and a solution delivery channel for delivery of the coating solution from a source to the nozzle. The substrates to be coated are mounted onto the substrate mounts, and the rotation member is rotated about its central axis to position one or more substrates at the coating station. The substrate mounts are rotated about the radial axes to rotate the substrates at a uniform rate during the coating process. During the coating process, the nozzle of the coating station is moved in a direction parallel to the substrate at a predetermined rate and is positioned a predetermined distance from the substrate to form a uniform coating on the substrate.
The invention provides a combination of advantages, including the ability to adjust or accommodate for surface geometries of a substrate to be coated, as well as the ability to provide substantially uniform coatings on such substrates. The invention eliminates human factors in the coating system, and allows for increased throughput of coated substrates. Further, the invention provides a reduction of coating solution waste during application of one or more coating solutions. According to the invention, substrates mounted on the rotation member can be expeditiously moved through a coating zone in sequence by the rotation of the rotation member, thereby reducing overall processing time. Additionally, the rotation of the substrate about second axes (e.g., radial axes or axes that are parallel to the central axis) during the coating process assists in achieving a uniform coating on the substrate.
The invention provides a device that is easy to use. The substrate mounts can be removable, so that an operator can easily insert and remove the substrates without disassembling the apparatus. The invention also eliminates variability in such parameters as coating thickness that can result from variations in substrate positioning on the holding apparatus. The invention allows positioning of the substrate in a manner that is substantially parallel to the coating station for coating.